MODIFICATION OF WEI & YAN APPROACH TO CONGESTION BY FACET ANALYSIS

One of the congestion models in DEA is WEI & Yan model. In this model technical efficiency out of pure technical efficiency determines the units that have weak congestion. In Wei & Yan model due to the probable turning to zero of the weight all of the units that have weak congestion will not be displayed. In this paper we will prevent the probable turning to zero of weights by facet analysis. Thus, through finding upper bound for free variable of v0 it is possible to prevent the probable weight turn to zero. So that the DMUs that are on weak frontier head into efficiency frontier. Finally the numbers of DMUs with weak congestion are expected to be specified exactly.